Process for extracting and separating cadmium



July 26, 1932.

S. HUGHES ET AL PROCESS FOR EXTRACTING AND SEPARATING CADMIUM Fe (5 o Cd, BEARING MATERIAL Original Filed July 29. 1927 V: v Cd 50 INSOLUBLE Fe(OH) AND AND F- COMPOUNDS 0F SUCH AS Fe- AND As Cu, A5 Bl, Pb

Fe, H5, AND A5 OADMIUM SULPHIDE V.

r {I Got 50 PRECIPITATE OF SMALL AMOUNTS or 5 I Pb, "11

OXIDIZING AGENT AND Ll M E.

PRECIPITATL 0F Cd 504 m"); /=6 As (14 ELECTROLYZE IN VEN TOR-S A TTORNEYS.

Patented July 26, 1932 UNITED STATES PATENT OFFICE STANLEY HUGHES AND ROSCOE TEA'IS, or DENVER, COLORADO, AssIGNoRs 'ro AMERI- CAN SMELTING AND BEFINING COMPANY, or NEW YORK, N. Y., A CORPORATION or NEW JERSEY PROCESS FOR E XTRAC'I'ING AND SEPARATING GADMIUM Application filed July 29, 1927, Serial Nazoass'z. Renewed September 30, 1931.

This invention relates to the separation of metals and more particularly to the separation and recovery of cadmium from ores, furnace products, flue dusts, baghouse dusts and 1; other materials in which the cadmium is present as anoxide, arsenate, arsenite, carbonate or other oxyacid.

The invention provides for the production of cadmium sulphate from any of the above mentioned cadmium compounds while preventing loss of cadmium due to the combination of oxides thereof with free oxides of arsenic that may be contained in the material. In addition to converting substantially the entire cadmium content of the ore, dust or other material being treated, into a soluble cadmium sulphate, various other elements such as iron and arsenic are largely prevented from going into solution and from contaminating the same. The cadmium sulphate solution may however, contain'small amounts of iron, copper, silver, bismuth,-lead, arsenic, mercury and antimony which are subsequently separated and removed, leaving a solution from which the cadmium may be recovered byelectrolysis or other well known means.

The invention further consists in'the new and novel features of operation and the new and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims.

Although the novel features whichfare believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objectsand advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description in which a particular commercial embodiment thereof is disclosed. It will be understoodhowever,that the processes and the steps thereof may be modified in various respects without departing from the broad spirit and scope of the invention.

In the following description and in the claims, the various steps in the process and the details comprising the invention will be identifiedby specific names for convenience but they are intended to be as generic in their application as the art will permit,

The accompanying drawing forming a part of this specification is a flow sheet illustrating the various steps in the process.

In the practice of this invention, the raw materials such as ore, furnace products, flue dusts, baghouse dust and the like from which the cadmium is to be recovered are preferably finely ground and mixed with' ferric sulphate and water. The mixture is then heated to the boiling point and agitated until the chemical reaction between the cadmium, ferric sulphate andwater is'completed;

The cadmium. present as cadmium oxide and cadmium carbonate reacts chemically with the ferric sulphate and water to form cadmium sulphate and ferric hydroxide. The cadmium combined with arsenic as arsenites and arsenates reacts chemically with the ferric sulphate to produce cadmium sulphate and insoluble compounds of iron and arsenic The cadmium sulphate produced in the above reactions is soluble in waterbut the ferric hydroxide and compoundsjof iron and arsenic are insoluble in water, and are separated from the cadmium sulphate solution by decantation or filtration! Ferric sulphate maybe either purchased on the market or may be produced by oxidiz "ing a ferroussulphate solution by any well I 'known meanssuch as bydissolving the'ferrous sulphate in water and passing'through the solution a mixture of air and sulphur dioxide in finely divided bubbles.

When the cadmium sulphate solution is separated from the insoluble compounds of iron and otherin'soluble constituents ofthe raw dust, it may contain small amounts of iron, copper, silver, bismuth, lead, arsenic,

.mercury and antimony. The'copper, silver,

bismuth, lead andmercury maybe precipltated from the cadmium sulphate solution by the addition of cadmium sulphide, which precipitates all of these elements as sulphides.

The remaining small amounts of iron and the amount required to make ferric arsenate.

The cadmium sulphate solution, having been freed from all the above mentioned impurities, is ready for electrolysis. Any zinc that may be present in the dustis converted to zincsulphate by the ferric sulphate, and remains in the solution along with the cadmium. The solution is electrolyzed by circulating in electrolytic cells,-using insoluble anodes of leader ferrosil-ioonandcadmium cathodes that have previously been deposited electrolytically as a sheet on aluminum cathodes. Due to the selective" action'b'etween the zinc and cadmium, thelatter element will be largely removed before the zinc deposits on the cathode. Hence by: 1 suitably controlling the electrolysis, theseparation ofthe ca'dinium from the solutionzmay be' substantially completed and the zinc allowed to remain in the electrolyte. V

The-following are believed tobe theequa- .tions of the principal chemical reactions used in thisprocess:

3Cd0 Fe '('SO4)3+3H O=3CdSO 2Fe (OH-)3 ecasoi 3H 0=3Cd 313 -80 +30-By electrolysis 21% +.-2H SO =2FeSO 4H 2F8S04 so2 -2O=Fe (.SO 2Fe (OH) AS2103: 2reAso +1 31120 are'ton As oF'areiiso.1 i Brno ca (AS0011 Fe (SO ).-,="3CdSO are-Mo4 .After the cadmium has been removed by means of electrolysis the sulphuric acid in the electrolyte may beemployed to dissolve scrap iron for forming additional quantities of ferrous sulphate Which may then *beconverted to ferric sulphate .and utilized for forming additional quantities of cadmium sulphate.

' By means of the present process,- cadmium which is presentin oxidized state as cadmium arsenate, arsenite or carbonate is readconverted to cadmium sulphate from whence. the cadmiummay be recovered-substantially free 'from impurities." "This process prevents the combination of oxides of. cadmium and arsenic and prevents .loss of cadmium .ars-enite and arsenate Which are only slightly soluble 'in wateroand Would other- Wise :go intol the, residues from the leaching tanks. "The ferric sulphate maybe readily manufactured from Waste materials Without adding materially to the expense of operation.

. 'A-lthough. certain novel features of the .in-

vention have been shown and :describe'dand are pointed out in theannexed claims, it will be understood that various omissions, substitutions and changes in the severalstepsof the process and in its operationamaybe made bythose skilled .in the art vvi'thoutldeparting "from the spirit of the invention.

. leaching said compounds with ferric sulphate to produce cadmium sulphate solution, removing the insoluble impurities by filtration and recovering cadmium therefrom.

2-. The process of extracting cadmium from materials containing cadmium as an oxide, arsenite, ;.arsenate,- carbonate. or similar compounds Which comprises leaching said compound With ferric sulphate and Water to produce a cadmium sirlphate seltttion,

removing 5 impurities from the -stil-ution by filtration and recovering cadmium from the filtrate.

3fT-he process (Sf "recovering cadmium from ores and other materials containing oxyacids of cadmium which comprises mixing the finelyidi-vided :materialwith a ferric sulphate solution and: heating untilthecadmium is oxidized and. forms. cadmium sul tphate, removing insoluble compoundsofiron silver,.bismuth, lead and mercury from the solution as asulphide precipitateitheaddition ofcadmium sulphide. and recovering cadmium from the solution.

and arsenicby filtration, removing.copper,r

4. The a process of recovering. cadmium$ from its .oxy compounds, which comprises mixing said. material '-With I ferric .sulphate solution, heating. the mixture to form. cad- .mium sulphate, removing insoluble .com-

pounds of iron and arsenicby filtratiomiadd-fi ing cadmium sulphide .to: remove-copper, silver, bismuth, lead .and mercury asisulphide precipitates, precipitating :the remaining iron with lime 'removing cadmium fro1n,the

solution. 4

- 5. The ,process-of recovering cadmium from its oxy compounds, which comprises leaching I said materials with; ferric sulphate solution to form cadmium sulphate, removing insoluble compounds :of .iron-"andarsenic byfiltratiomadding cadmium sulphide to remove copper, silver, bismuth, lead .andmer- .cury as "sulphide precipitates, removing; the remaining. iron and arsenic. by. precipitating :the ironwith lime whereby the said .precipi-- mixing said: materials with. .ferricsulphate solution, heating the. mixture to'aformwcadmium sulphate, removing insoluble ..com- M pounds of iron and arsenic. .filtration add ing cadmium sulphide :torremove copper, silver, bismuth, lead. and mercury as sulphide precipitates, removing the. remainingv iiron and arsenicby oxidizing the iron. and zpre cipitating the iron with: lime. 'Wherebytthe said precipitate may combine with (there- Hmaining arsenic and removing .cadmium* i from thesolution. I V l 1 7. -.The process of recover-ing zcadmium from its oxy. compounds, which "comprises .mixing. said materials with ferric sulphate solution, heating the mixture.-to,-form:.cad-* mium sulphate, removing insoluble compounds of iron and arsenic by filtration, adding cadmium sulphide to remove copper, silver, bismuth, lead and mercury as sulphide precipitates, removing the remaining iron and arsenic by oxidizing the iron with sodium chlorate and precipitating the iron with lime whereby the said precipitate may combine with the remaining arsenic and removing cadmium from the solution.

8. The process of recovering cadmium from its oxy compounds, which comprises mixing said materials in finely divided condition with ferric sulphate and water, heating and agitating until the cadmium is oxidized and forms cadmium sulphate, removing insoluble compounds of iron and arsenic by filtration, adding cadmium sulphide to remove copper, silver, bismuth, lead and mercury as sulphide precipitates, removing the remaining iron and arsenic by oxidizing the iron with sodium chlorate and precipitating the iron with lime whereby the said precipitate may combine With the remaining arsenic and removing cadmium from the solution.

9. The process of extracting cadmium from its oxy compounds which comprises leaching said compounds with ferric sulphate solution to produce a cadmium sulphate s0- lution, effecting a separation between insoluble impurities and the cadmium sulphate solution and recovering cadmium from the latter. 7

In testimony whereof we have hereunto set our hands.

STANLEY HUGHES.

e ROSGOE TEATS. 

